Method and apparatus for automatically aligning electrical circuits



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BY J2 l l I l I. Wwvlwb LCN QNX@ Patented Jan. 29, 1952 OFFICE METHOD AND APPARATUS FOR AUTOMATI- CALLY ALIGNING ELECTRICAL CIRCUITSv Kurt Enslein, Rochester, N. Y., assigner to Stromberg-Carlson Company, a corporation of New York Application April 20, 1950, Serial No. 157,160

The present invention relates to methods of and apparatus for adjusting electrica1 circuits, and, more particularly, to a method and apparatus for automatically aligning resonant circuits to a predetermined frequency. While my invention is of general utility, it is particularly suitable for use in the mass production of radio and television receivers, especially in connection with the alignment of the resonant circuits thereof.

In many instances, it is desirable to perform alignment operations upon electrical circuits by means of automatic apparatus which may be operated by untrained or semi-skilled operators. For example, in the mass production of radio and television receivers, the resonant circuits of the receiver must be tuned to the correct operating frequencies. Conventionally, the alignment of such resonant circuits is performed by trained operators, each operator being provided with expensive signal generators which sweep through the desired band of frequencies, the operator viewing the response curve produced thereby on'an oscilloscope and manually adjusting the tuning of each resonant circuit to the correct frequency as seen on the oscilloscope. Such procedure in aligning the receiver is inherently laborious and time consuming and requires skilled personnel to manipulate and interpret the data obtained from the test equipment. Additionally, a separate testing station with its associated sweep generators, cathode ray Oscilloscopes and other equipment must be provided for each assembly line, inasmuch as each operator requires a separate test signal which may be tuned through the desired band of operating frequencies.

It is, accordingly, an important object of the present invention to provide a new and improved method of and apparatus for automatically aligning electrical circuits to a predetermined frequency.

It is another object of the present invention to provide a new and improved method of and apparatus for automatically aligning electrical circuits to a predetermined frequency which method and apparatus are particularly suitable for use by unskilled operators on a production line basis.

It is a further object of the present invention to provide a new and improved method and apparatus for automatically aligning electrical circuits to a predetermined frequency without the use of sweep frequency generators or other complicated alignment equipment.

19 Claims. (Cl. Z50- 40) It is a still further object of the present invention to provide a new and improved method and apparatus for automatically aligning electrical circuits to a predetermined frequency wherein fixed frequency sources may be utilized for an entire mass production receiver assembly plant.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the following specification taken in connection with the accompanying drawings in which:

Fig. 1 is a schematic diagram in block form of an automatic alignment apparatus constructed in accordance with principles of the present invention;

Figs. 2, 3, 6 and "IA are diagrams showing wave forms which occur in certain portions of the apparatus of Fig. 1; and

Figs. 4, 5 and 8 through 10 are detailed schematic diagrams of portions of the automatic alignment apparatus of Fig. l.

Referring now to the drawings, there is illustrated in Fig. 1 in block diagram form, an automatic alignment apparatus suitable for practicing the method of the present invention. The modulated carrier wave receiver, the resonant circuits of which are to be aligned to the proper operating frequency, is illustrated generally at I0 and a xed frequency alignment signal generator I I is connected to the terminals I2 and I3 of the receiver I0. The receiver I0 may include a plurality of resonant circuits which are to be aligned to the correct operating frequency, one of these circuits being illustrated at I5. For example, the resonant circuit I5 may be contained in the intermediate frequency channel of the modulated carrier wave receiver under test. As shown, the

resonant circuit I5 comprises an inductive branch I6 and a capacitive branch I'I and the resonant circuit I5 is associated with the second detector I8 of the receiver. As is customary, the second detector circuit includes a load resistor I9 and an associated lter capacitor 2| which are connected in series with the detector I8 and resonant circuit I5 and operate as a load circuit across which appears the detected voltage.

While the resonant circuit l5 may be energized by any suitable means from the preceding stage in the receiver, in the illustrated embodiment the inductance I6 is shown as the secondary winding of an interstage transformer 22, the primary of transformer 22 being connected to the anode of the preceding amplifying device 23. In this connection it will be understood that the device 23 is supplied with a signal at the fixed frequency of the alignment signal generator II through the intermediate stages of the receiver between the input terminals I2 and I3 and the device 23. Alternatively, the alignment signal from the signal generator I I may be directly connected to the input circuit of device 23 in the event that the preceding stages are mistuned by an amount sufcient substantially to prevent transmission of the alignment signal through the intermediate stages, as will be readily apparent to those skilled in the art.

The resonant frequency of the circuit I5 may be varied by any suitable means. For example, the inductive branch I3 of the resonant circuit may be varied by means of a powdered iron tuning slug 2d which threads into the coil I6 so as to change the inductance thereof and hence the resonant frequency of the Circuit l5. In order to align the resonant circuit I5 to the frequency of the alignment signal by fully automatic means which may be utilized by semi-skilled or unskilled personnel, there is provided means for automatically threading the tuning slug 24 into and out of coil I6. More specifically, there is provided a driving member 25 which may comprise any suitable tool, such as a screw driver, or the like, which engages the screw driver slot in the tuning slug 24, and which is driven through a flexible drive shaft S from a reversible driving means 2Q, controlled in accordance with the principles of the present invention. The driving member 25 may be engaged with the tuning slug either manually by the operator or by means of automatic or semi-automatic positioning apparatus.

In order to provide a suitable signal for controlling the operation of the reversible driving means 2E there is derived from the second detector load circuit I9 and 2| a signal voltage which varies with the tuning of the resonant circuit I5. Thus, the output from the second detectorl I8 is connected through the conductor 26 to the input of a discriminating amplier 35. The output of the discriminating ampliiier 35 is connected to a pulse-shaping circuit 3S and the output of the pulse-shaping circuit S is connected through a sensing circuit 3l to the reversible driving means 2t. The output of the pulse shaping circuit 36 is also connected through a pulse counter circuit 38 to the reversible driving means 20.

To align the circuit I5 to the correct operating frequency, the reversible driving means 20 moves the tuning slug in a predetermined direction until the tuning of the resonant circuit I5 is passed through the peak resonance point Which occurs at the frequency of the alignment signal. A control pulse indicative of the passage of the tuning of the resonant circuit I5 through the maximum response point is then utilized to reverse the driving means 20 so as to bring the tuning slug back to the correct peak resonance position. In the event that the driving means 2i) causes the tuning slug to be moved too far in the opposite directions, a further control puise is derived to reverse the driving means again, the driving means 20 being reversed by successive control pulses a sufiicient number of times to bring the tuning slug into the correct position. Inasmuch as the tuning slug is brought approximately to the correct position upon the second reversal of the driving means 20, the pulse counter circuit 38 is provided to limit the number of times the driving means is reversed and hence the time consumed in moving the tuning slug to the correct position.

Considering now the operation of the abovedescribed alignment apparatus as a Whole, and Without referring specifically to individual circuit arrangements suitable for providing the above discussed signals, as the tuning slug is moved in a particular direction by means of the driving member 25, the voltage across the detector load circuits Iii and 2i increases as the resonant frequency circuit I3 comes closer to the frequency of the alignment signal supplied to the circuit IG between device 23. When the resonant frequency of the circuit I5 coincides with the alignment signal frequency the voltage developed across the detector load circuit is at a maximum value, and as the tuning slug moves further in the same direction the voltage decreases as the frequency of the circuit I5 moves further away from the peak resona-nce point. Thus, as illustrated in 2, the signal voltage from the detector load resistance may be plotted in terms of the position of the tuning slug and takes the form of a conventional single humped resonance curve 313, the maximum or peak resonance point B being coincident with the alignment signal frequency f. In this connection it will be understood that t e second detector I8 is polezi with respect, to ground so as to produce a negative potential with respect to ground across the detector load circuit I3 and 2|. Still referring to Fig. 2, it is evident that the slope of the resonance curve varies from a large negative value to a large positive value during the complete travel of the tuning slug in a particular direction. Thus, the slope of the resonance curve 33 with the tuning slug in an initial position A has a large negative value, the slope of the resonance curve at the peak resonance point B is equal to zero, and the slope of the resonance curve 3i) at the end position C of the tuning slug has a large positive value. If, now, the tuning slug is moved from the initial position A to the final position C by the reversible driving mea-ns 20, a voltage proportional to the portion of the esonance curve between the positions A and C Will be produced across the detector load circuits 26 and 21.

To provide a control signal which is indicative of the passage of the resonant circuit I5 through peak resonance, which signal may be used to reverse the driving means 25 after passage through the peak resonance point, the discriminating amplier 35 is arranged to diiierentiate the voltage wave appearing across the detector load circuit. In this connection, it Will be understood that differentiation of the control Wave form produces a voltage which is equal to the rate of change, or, in other words, the differential, of the initial wave form 353. If the Wave form appearing across the detector load circuit as the slug is moved in a predetermined direction is diierentiated, there are provided positive and negative pulses vwhich correspond to the changes in slope of the response curve 3S. Thus, if the tuning slug is moved in the direction of the arrow 4Q, shown in Fig. 3(a), the Wave form 4I is produced. The differential Wave form I comprises a first negative peak 42 which corresponds to the large negative slope of the response curve at position A thereon and a positive peak 43 which corresponds to the large positive slope of the response curve at position C. Intermediate the negative and positive pulses 42 and .'13 the response curve intersects the desired resonant frequency f, this intersection point corresponding to the position B shown in Fig. 2. It is thus evident that the positive pulse 43 of the differential Wave form 4I isindicative of the passage of the resonant circuit through the peak resonance point, inasmuch as the initial portion of this positive pulse corresponds to the intersection of the wave form 4| with thedesired resonant frequency f.

Considering now the differential wave form produced by the discriminating amplifier 35 when the tuning slug is moved in the opposite direction, illustrated by the arrow 45 in Fig. 3b, it is evident that the differential wave form 45 is reversed from the wave form 4| produced in Fig. 3a, and is provided with a negative pulse portion 41 followed by a positive pulse portion 48. However, the positive pulse portion again follows the intersection of the differential wave form 45 with the resonant frequency f so that the positive pulse portion may be utilized to reverse the direction of movement of the tuning slug regardless of the initial direction thereof.

The discriminating amplifier 35 not only di-fferentiates the wave form appearing across the detector load circuit to provide the above-described differential wave form, but also selects the positive-going pulse portion of the differential wave lform and rejects the negative pulse portion thereof. The vamplifier 35 thus discriminates against the unwanted portion of the differential wave form. In order to reverse the driving means promptly after passage through the peak resonance point and to the end that the tuning slug may be brought to the correct position in a minimum of time and with a minimum number of reversals in the direction of movement thereof, there is provided the pulse shaping circuit 36 which acts upon the selected positive pulse portion of the differential wave form to provide a control pulse of negative polarity, the leading edge of which corresponds approximately to the crossover or intersection point o-f the differential wave form with the desired alignment frequency. The negative pulse from the pulse shaping circuit 36 is supplied to the sensing circuit 31 which operates as an electronic switch and reverses the driving means for each control pulse supplied thereto.

Inasmuch as the tuning slug is brought to approximately the correct position upon the second reversal of the driving means 20, the total number of reversals of the driving means 2!) may be limited so as to accomplish the desired alignment as quickly and efficiently as possible and with aminimum amount of time expended by the operator. To this end, there is provided the pulse counter circuit 38 to which are supplied pulses from the pulse shaping circuit 35. The pulse counter circuit 38 c-ounts the number of pulses appearing at the output circuit of the pulse shaping circuit 36 which pulses correspond to reversals of the driving means 20, and deenergizes the driving means when a predetermined number of pulses have occurred.

In considering specific embodiments of the circuits indicated in block diagram form in Fig. l, reference is now made to Fig. 4 wherein there is shown in detail a discriminating amplifier suitable Ifor providing the above-described control signal. As shown, the output from the detector load circuit is connected through a capacitor 50 to the control electrode of an electron discharge device 5i. The control electrode of device 5| is connected through a resistor 15 to ground potential. The anode of device 5| is connected to a positive source of unidirectional potential indicated by the legend B+,the cathode of device 5| being connected through a resistor 6 52 to the negative terminal of a unidirectional source of potential indicated as the battery 53. The cathode of device 5| is also connected to the cathode of a second electron discharge device 54, the control electrode of device 54 being con- Knected *to ground. The anode of device 54 is connected through an anode load resistor 55 to the B+ supply and is further connected through a capacitor 56 to the control electrode of a pentode type electron discharge device 51. The control electrode of device 51 is connected through resistors 58 and 59 to the negative terminal of battery 53, the junction point of resistors 58 and 59 being connected through a further resistor 58 to ground potential. The anode of device 51 is connected through anode load resistor 6| to the B+ supply and there is provided a screen electrode dropping resistor 52 between the B+ supply and the screen electrode of device 51. The output from the anode of device 51 is connected through a capacitor 63 to the succeeding pulse shaping circuit 36.

In considering the operation of discriminating amplifier 35, reference may be had to Fig. 6 wherein there are illustrated wave forms which appear in certain p-ortions of the amplifier 35. Thus, referring to Fig. 6, the wave form which is produced across the detector load circuit is illustrated by the wave form 65 and it is evident that the wave 65 is in the form of a single peaked resonance curve. The wave form 55 is supplied to the input circuit of the device 5| (Fig. 4) wherein it is differentiated to provide the differential wave -form 65 illustrated in Fig. 6, the capacitor and resistor 10 which comprise the input circuit of device 5| being of sufficiently small value to provide the necessary differentiating action. The device 5| is operated as a cathode follower and consequently the device 5| is able to follow the positive and negative portions of the differential wave form without loading downthe input circuit as will be readily apparent to those skilled in the art. The output of cathode follower 5| is directly connected to the device 54 which is operated as a grounded grid amplifier. Inasmuch as the phase of the input signal does not change in either of the devices 5| or 54, the differential wave form 66 is repeated in similar phase to the input circuit of the device 51. However, due to the biasing action of the control electrode network comprising resistors 58, 59 and 60, the control electrode of device 51 is operated at approximately the anode current cutoff point so that the negative pulse portion 61 of the differential wave form 65 (Fig. 6) is removed and a sharp negative pulse 69, which corresponds to the positive portion 58 of the differential wave form 55, appears in the output circuit of the discriminatingr amplifier 35.

While the selected negative pulse 59 is a rough indication of the slope reversal of the control wave 65, and hence a rough indication of the passage of the resonant circuit through the desired peak resonance point, it is necessary to square up the pulse '59 so as to provide a pulse, the leading edge of which will correspond almost exactly to the crossover point of the differential wave form 66. Such shaping action is provided by the pulse shaping circuit 3B which is illustrated in Fig. 5. Thus referring to Fig. 5, the negative pulse from the output of the discriminating amplifier 35 is supplied to the control electrode of a pentode type electron discharge device 15. The control electrode of device 15 is connected through a resistor 16 to ground and the anode of device 15 is connected through an anode load resistor 11 to the B+ supply potential. Voltage appearing at the anode of device 15 is coupled through capacitor 18 to the control electrode of a pentode type electron discharge device 80. The control electrode of device 80 is connected through resistors 8| and 82 to the negative terminal of the battery 83 and the junction point between resistors 8| and 82 is connected through a resistor 84 to ground potential. The anode of device 80 is connected through a resistor 85 to the B+ supply and voltage appearing at the anode of device 80 is coupled through capacitor 86 to the output terminal 81 and thence to the sensing circuit 31. The capacitor B is also connected to the control electrode of an electron discharge device 88 which inverts the pulse supplied thereto and supplies a pulse of opposite polarity from the anode circuit thereof through the capacitor 89 to the pulse counter circuit 38.

Considering now the operation of the abovedescribed pulse shaping circuit, it is evident that the device 15 is operated at zero bias so that the negative-going pulse 69 drives the device 15 beyond anode current cutoff and hence the most negative portion of the pulse E9 is removed by grid clipping. The pulse 69 thus appears in the anode circuit of device 15 as a iiat-topped positive-going pulse 90 (Fig. '7). The input circuit of device 80, which comprises capacitor 18 and resistor 8|, is so chosen that the flat-topped pulse 90 is differentiated so as to provide at the control electrode of device 80 the wave form illustrated at 9| in Fig. '7. Thus, the differentiated wave form 9| comprises a positive pulse portion 92 which corresponds to the leading edge of the pulse 90, and a negative pulse portion 93 which corresponds to the trailing edge of the pulse 90. The control electrode Of device 80 is operated at the anode current cutoff point, by means of the bias network including resistors 82 and 84, so that the negative-going pulse 93 of the differentiated wave form 9| is removed by grid clipping and there is provided in the anode circuit of device 80 a negative-going pulse 94 which coincides in time with the crossover point of the original differentiated control wave form 03 (Fig. 6). From the foregoing, it is evident that the discriminating amplifier and pulse ,f

shaping circuits described above diierentiate and clip the initial response curve to provide a control pulse 59 which is indicative of the passage of the resonant circuit through the desired peak resonance point. The control pulse 69 is amplied and is differentiated so as to provide a second control pulse 94 which coincides in time almost exactly with the change in slope of the original resonance curve 65. The second control pulse 94 is then used to control the sensing circuit 31 and through the phase inverter 88 to control the pulse counter circuit 38.

In order to reverse the driving means 20 in response to successive control pulses from the pulse shaping circuit 36, there is provided the sensing circuit illustrated in Fig. 8. As shown, the sensing circuit 31 comprises a pair of electron discharge devices and |0|. The devices 00 and |0 are arranged to be switched abruptly from a conductive to a non-conductive state, or vice versa, in response to successive ones of the control pulses 91| supplied thereto from the pulse shaping circuit 36. The devices |00 and |0| are thus arranged in an electrical circuit, which is generally referred to as a iiip-iiop circuit, or

trigger circuit commonly known as an Eccles- Jordan circuit, this circuit being modified in the manner to be described hereinafter to provide proper operation in response to the negative control pulses 94 supplied from the pulse shaping circuit.

The control pulses from the pulse shaping circuit are supplied over conductor |02 and through capacitors |03 and |04 to the suppressor electrodes of the devices |00 and |0|, respectively. The suppressor electrodes of these devices are respectively connected to ground through the resistors |05 and |05. The anode of device |00 is connected through an anode load resistor |01 to the B+ supply and the anode of device |0| is connected through an anode load resistor |00 to the B+ supply. Screen dropping resistors |03 and ||0 are provided between the B+ supply and the screen electrode devices of |00 and |0|, respectively, The anodes of devices |00 and |0| are cross-connected to the control electrode of the other device through the networks and ||2. Thus the anode of device |00 is connected through network to the control electrode of device |0|. Also, the anode of the device |0| is connected through network I|2 to the control electrode of the device |00. The control electrodes of devices |00 and |0| are connected respectively through resistors I|3 and ||4 to the negative terminal of a battery ||5, the positive terminal of battery ||5 being connected to the ground. The control electrodes of devices |00 and |0| are also connected respectively to ground through resistors ||8 and |I1.

In considering the operation of the sensing circuit 31 in response to negative control pulses from the pulse shaping circuit 3B, it will be understood that when one of the devices |00, |0| is conducting it will provide sufiicient bias voltage to hold the other device beyond cutoff. Thus, assuming that device |00 is in a conductive state, the flow of current through the anode load impedance |01 associated therewith produces a sufcient voltage drop through the bleeder network comprising the resistive branch of the network the resistor ||4 and the battery ||5 to hold the device |0| in a non-conductive state. In this connection it will be understood that the values of resistor |01, the resistive branch of network and resistor ||4 are chosen so that correct negative bias potential appears at the control electrode device |0| when the device |00 is in a conductive state. If, now, it is assumed that a negative control pulse is supplied to the suppressor electrode of device |0| through capacitor |03, the device |0| is abruptly switched to a nonconductive state. This causes a rise in potential at the anode of device |00 and a corresponding rise in potential at the control electrode of device |0|, so that the device |00 conducts. When the device |0| conducts, the drop through its anode load resistor |08 produces a negative p0- tential which biases off the control electrode of device |00 through the network ||2 and the resistor ||3. The device |00 is thus switched from a. conductive to a non-conductive state in response to a first control pulse from the pulse shaping circuit 33. At the same time the device |0| is switched from a non-conductive to a conductive state.

The next succeeding control pulse from the pulse shaping circuit is coupled to the suppressor electrode of device |0| through the capacitor |04 so as to switch the device |0| abruptly from a conductive to a non-conductive state, the device f |26 and |21.

| at the same time being placed in its initial conductive condition. Successive negatlve control pulses applied to the suppressor electrodes of the devices lili? and IUI operate to switch the devices abruptly from a conductive to a non-conductive state and vice versa. lt is thus evident that the potenti-als which appear at the control electrodes of the devices |00 and |0| are of substantially uniform magnitude between pulses and abruptly switch from one value to the other in response to the control pulses from the pulse shaping circuit. Accordingly, the control electrode potentials of devices |00 and |0| may be used to control the reversible driving means 20 shown in Fig. 1. Thus, the control electrode potential of device is connected through the conductor H3 to the reversible driving means 20 and the control electrode potential of device |0| is similarly connected through the conductor |9.

In Fig. 9 there is illustrated a reversible driving apparatus suitable for moving the tuning slug of the receiver under test in the desired directions. As shown, the reversible driving means ,comprises a pair of electron discharge devices |20 and |2|. The control electrode of device |20 is connected to the sensing circuit 31 through an isolating resistor |22 and the conductor IIS. Likewise the control electrode of device |2| is connected to the sensing circuit through an isolating resistor |23 and the conductor H8. To

drivek the tuning slug in the required direction,

there is provided a reversible D. C. motor having an armature |25 and a pair of eld windings Energzation of the armature |25 is controlled by the counter circuit 33 and will `be described in detail in connection therewith. The flow of current through the windings |26 c and |21 is controlled by means of the devices |20 and |2| so as to control the direction of rotation vof the armature |25 and hence the direction of potentials appearing at the control electrodes of the sensing circuit control devices. Thus, considering the above-described situation wherein the devicey |09 of the sensing circuit is in a conductive state and the device |0| is in a non-confductive state, the control electrode of device |00 is at a relatively high positive potential so that the device |2| of the reversible driving means is also placed in a conductive state and current iiows through the winding |21 so .as to produce rotation of the armature |25 in a given direction. AWhen a control pulse appears in the output of the pulse shaping circuit in response to passage of the resonant circuit through the maximum tuning point, the control devices of the sensing circuit `arejabruptly switched from a conductive to a non-conductive state and correspondingly the device |2| is rendered non-conductive and the device |20 is placed in a conductive state. With the device |23 conducting, current flows through the eld winding |26 and causes rotation of the armature in the opposite direction. It is thus evident that successive control pulses from the pulse shaping circuit 36 operate to switch the current ilow from one eld winding to the other so that the armature |25is reversed in response thereto.

In order that the alignment of the resonant circuit may be accomplished in a minimum amount of time, the number of reversals of movement of the tuning slug is limited 'by means of the electronic counter circuit shown in Fig. 10. Thus, referring to Fig. l0, positive control pulses from the phase inverter 88 of the pulse shaping circuit 36 are supplied through a capacitor |30 to the control electrode of an electron discharge device' |3|. The control electrode of device |3| is connected through resistors |32 and |33 to ground potential, the junction point of resistors |32 and |33 being connected through a resistor |34 to a negative source of unidirectional potential. The anode of device |3| is connected through an anode load resistor |35 to the B+ supply and is also connected through a capacitor |36 to the control electrode of `an electron discharge device |31. The control electrode of device |31 is connected to ground through a resistor |38. The anode ci device |31 is connected through a load resistor |39 to the B+ supply and is further connected through a capacitor |400. to the control electrode of device |3|.

The devices I 3| and |31 operate as a multivibrator which is normally held inoperative by means of the bias network including resistors |33 and |34. However, positive pulses which are supplied to the pulse counter circuit 38 from the phase inverter tube 88 of the pulse shaping circuit 36 operate to trigger the multivibrator thus initiating one complete cycle of operation thereof. Thus, considering the application of a positive pulse through the capacitor |30 to the control electrode of device 3|, the device 3| is caused to conduct maximum anode current, the oorresponding drop in voltage across the anode load resistor |35 being coupled to the control electrode of device |31 so as to render that device non-conductive. When the charge on the coupling capacitor |36 is drained oi through the associated grid leak resistor |38, the device |31 again conducts and the devices are switched abruptly to their initial position with the device |3| again in a non-conductive state. The multivibrator comprising devices |3| and |31 thus operates to provide at the anode of device |3| a negative-going square wave, the leading edge of which coincides in time with the output pulses from the pulse shaping circuit.

The output of the multivibrator which includes tubes |3| and |31 is coupled to a rst trigger circuit which includes a pair of electron discharge devices |40 and 4|. The anode of device |40 is connected through a first load resistor |42 and a second load resistor |43 to the B+ supply. Likewise the anode of device I 4| is connected through a resistor |44 and the resistor |43 to the B+ supply. To connect the multivibrator to the trigger circuit |40 and |4|, there is provided a capacitor |45 which is connected from the anode of device |3| to the junction of resistors |42,v |43 and |44. The rst trigger circuit including devices |40 and |4| is of the general type referred .to as a flip-.op circuit, in which the electron discharge devices are arranged to be switched Aabruptly from a conductive to a non-conductive state, or vice versa, in response to control pulses of a given polarity. However, unlike the multivibrator |3| and |31 previously described, the devices |40 and |4| of the rst trigger circuit Vremain in the condition to which they are 'switched until a succeeding control pulse is supplied to the circuit. To accomplish this, the devices are provided with interconnecting bleeder networks from the anode of one device to the 11 control electrode of the other device. Thus, the device |40 is connected through a resistor |46 to the control electrode of device |4| and thence to ground through the resistor |41. The control electrode of device |4| is also connected through a resistor |48 to a negative source o potential. Likewise, the anode device of |4| is connected through a resistor |46 to the control electrode of device |40 and thence through a resistor |50 to ground. The control electrode of device |40 is also connected through a resistor 15| to the negative source of potential. The values of the resistors included in the bleeder networks connected between the anode of one device and the control electrode of the other chosen that conduction of one device establishes a potential at the control electrode of the other device 'suliicient to bias the other device beyond cutoi. Thus, assuming that the device 40 is normally conducting, there is a flow of anode current through the resistors |42 and |43 so that the potential at the anode of device 40 has a relatively low value. The value of resistors |46, |41 and |48 are so chosen that the control electrode potential of device |4| is suiciently nega- 1 tive to bias that device beyond cutoff. To facilitate an abrupt switching action, there is provided across the resistor |46 a capacitor |51 and across the resistor |49 a capacitor |58. The capacitors |51 and |58 operate as a high frequency by-pass so that the high frequency components which occur during the switching operations are conveyed directly to the control electrode of the opposite device.

In considering the ip-iiop action of the trigger circuit, including devices and 14| when negative pulses are supplied to the trigger circuit from the previous multivibrator, it should iirst be mentioned that the negative square wave from the output circuit of the multivibrator is differentiated in the circuit including capacitor and the resistor' |43, so as to provide a sharp negative pulse which coincides with the leading edge of the square wave produced by the multivibrator and hence corresponds in time to the leading edge of the output pulse supplied to the multivibrator from the pulse shaping circuit. In this connection it will be remembered that the leading edge of the pulse from the pulse shaping circuit corresponds approximately in time with the passage of tuning of the resonant circuit through the maximum response point. A negative pulse corresponding to the leading edge of the multivibrator output wave is connected to both anode circuits of the devices |40 and |4| and through the bleeder network-s associated therewith to the control electrodes of the devices. This negative pulse which is supplied to the trigger circuit operates to cut off the particular one of the devices |40 and |4| which is conducting at that particular time and hence operates to switch the devices abruptly from a conductive to a non-conductive state and vice versa.

In order to render one of the devices |40 and I4| non-conductive so that the counter circuit may be re-set, there is provided a diode rectifier device |55, the anode of which is connected to the control electrode of device |4| and the cathode of which is connected through a switch |56 to the negative source of potential. switch |56 closed, the diode |55 is of the proper polarity to conduct and causes the control electrode of device |4| to be held at the negative supply potential. Thus, closure of the switch |56 and subsequent opening thereof insures that device are so With the E i2 the device |4| is normally non-conducting and that the rst control pulse indicative of passage of the resonant circuit throughout the maximum tuning point will switch the devices |40 and |4| in a predetermined sequence. 'I

In order to count a plurality of control pulses from the pulse shaping circuit and hence to provide for a plurality of reversals in direction of the movement of the tuning slug, there is provided a second trigger circuit, including a pair of electron discharge devices |60 and |6|. The devices |60 and |6I are controlled from the rst trigger circuit described above and the second trigger circuit is substantially identical in construction thereto. However, control pulses from the first trigger circuit are connected to the control electrode of the device |60 instead of being connected to the anode circuits of both devices as in the first trigger circuit. Thus, the anode of device |40 is connected through a capacitor |62 to the control electrode of device |60. The capacitor |62 and the associated resistance of the input circuit of device |60 are so chosen that the output wave from the first trigger circuit is differentiated as it is applied to the second trigger circuit.

The second trigger circuit, including devices |60 and I 6|, is also provided with means for insuring that a particular one of the devices is normally non-conductive. Thus, there is provided a diode rectifier device |65, the anode of which is connected to the control electrode of device |6| and the cathode of which is connected through a switch |66 to the negative source of supply. Closure of the switch of |66 places the control electrode of device I6| at the negative supply potential, thus insuring that the device |6| is normally non-conductive. In this connection, it will be understood that the switches |56 and |66 are opened before the counter circuit is to be used so as to allow the above-described switching action to occur in both the first and second trigger circuits.

In order to control the reversible motor means 20 in accordance with a predetermined number of pulses from the shaping circuit 36, there is provided a control device |10 in the anode circuit of which there is connected a relay winding |1|. The control electrode of the normally non-conducting device |4| of the first trigger circuit is connected through an isolating resistor |12 to the first control electrode |13 of the device |10. Likewise, the control electrode of the normally non-conducting device |6| of the second trigger circuit is connected through an isolating resistor |14 to the suppressor electrode |15 of the device |10. The screen electrode |16 of device |10 is connected to the B+ supply. Inasmuch as the control electrodes |13 and |15 of the device |10 are directly connected to the control electrodes of the normally non-conducting devices |4| and |6|, the device |10 is normally held in a nonconductive state with the contacts |11 and |18 associated with the relay coil |1| normally closed. When both the devices |4I and I6| are in a. conductive state, both the control electrodes |13 and |15 are at a positive potential with respect to ground and hence the device |10 permits a flow of current through the relay coil |1| to open the contacts |11 and |18. The contacts |11 and |13 are included in the armature circuit of the driving motor. Thus, the armature |25 of the reversible driving motor is connected from ground to the contact |11 and the contact |16 ls connected to a positive source of unidirectional potentlal suitable for energization of the armatermined number of motor reversals before deenergizing the armature thereof, it will be remembered that the devices |4| and |6| of the respective trigger circuits are conditioned for the counting operation by placing these devices in a. normally non-conductive state by momentary closure of the switches |56 and |66. The first negative pulse from the multivibrator comprising the devices |3| and |31, which corresponds to the rst pulse from the shaping circuit 36, switches the devices |40 and |4| so that the device |40 is non-conductive and the device |4| is in a conductive state. Switching of the device |4| to a conductive state causes the potential at the control electrode |13 of the device |10 to be at ground potential. However, the second control electrode |15 of device |10 is still at a large negative potential so that the device does not conduct and hence the relay contacts remain closed.

The second control pulse from the multivibrator switches the devices |40 and |4| back to their original position and in so doing the device`|40 is changed from a non-conductive to a conductive state. When the device |40 conducts due to the second control pulse supplied to the first trigger circuit, there is produced in the anode circuit of device |40 a negative pulse which is applied through the capacitor |62 to Athe device |60 and operates to switch the second trigger circuit. Simultaneously with the switching of the first trigger circuit back to its initial position the second trigger circuit is switched due to the above-mentioned connection of the device |40 to the device |60. Thus, the second control pulse causes the device |60 to berendered non-conductive andthe device |6| to be rendered conductive. With the device |6| conductive, the control electrode of device |10 is at ground potential. However, simultaneously with the switching of device |6| to a conductive condition, the device |4| is switched back to a nonconductive condition so that the control electrode |13 is at a large negative potential and the device 1|l remains in a non-conductive state.

Upon the occurrence of a third negative control pulse from the multivibrator, which corresponds to a third reversal in the direction of travel in the tuning slug, the rst trigger circuit is switched so that the device |40 is in a non-conductive state and the device |4| is conductive. Inasrnuch as both the devices |4| and |6-| are now conducting, the device |10 is rendered conductive and the relay coil opens the relay contacts 11 and |13 so that the armature circuit of the driving motor is deenergized. It Ais thus evident that the pulse counter circuit 38 responds to the third control pulse supplied thereto from the pulse shaping circuit and operates to cle-energize the driving motor upon the occurrence of the third control pulse. In this connection, it will be remembered that control pulses from the pulse shaping circuit are also supplied to the sensing circuit which operates to reverse the direction of travel of the driving motor for each control pulse so that the tuning slug is reversed in direction three times before the driving motor is de-energized.

While there is illustrated ak particular arrangement in which movement of the tuning slug is discontinued after three'reversals in the direction of movement thereof, it will be obvious that a different number of reversals may be utilized. For example, if sufficient gain is provided in the discriminating amplifier and pulse shaping circuit the tuning slug may be stopped at the second reversal of the driving motor. On the other hand, more reversals may be desirable to increase the accuracy of tuning to the alignment signal.

While there has been described what is at present considered to be the preferred embodiment of the invention, it will be understood that various modifications may be made therein which are within the true spirit and scope of the invention as defined in the appended claims.

What is claimed as new and is desired to be secured by Letters Patent of the United States is:

l. The method of adjusting the tuning of a resonant circuit to a predetermined frequency which comprises the steps of, energizing said circuit at said predetermined frequency, varying the tuning of said resonant circuit in a predetermined direction, deriving a signal from said resonant circuit indicative of the passage of said resonant circuit through said predetermined frequency and reversing the direction of tuning of said resonant circuit in response to said signal.

2. The method of adjusting the tuning of a resonant circuit to a predetermined frequency which comprises the steps of, energizing said circuit at said predetermined frequency, varying the tuning of said resonant circuit in a predetermined direction, deriving asignal from said resonant circuit indicative of the passage of said resonant circuit through said predetermined frequency, reversing the direction of tuning of said resonant circuit in response to said signal, and stopping said tuning variation at the maximum response point of said resonant circuit.

3. The method of adjusting the tuning of a resonant circuit to a predetermined frequency which comprises the steps of energizing said circuit at said predetermined frequency, varying the resonant frequency of said circuit in a predetermined direction, deriving a signal from said resonant circuit in response to passage of the resonant frequency of said circuit through said predetermined frequency, and reversing the direction of frequency variation of said circuit in response to said signal.

4. The method of adjusting the tuning of a resonant circuit to a predetermined frequency which comprises the steps of, energizing said resonant circuit at said predetermined frequency, varying the tuning of said resonant circuit in a predetermined direction, deriving a signal from `said resonant circuit proportional to the instantaneous frequency thereof, differentiating said signal to obtain control pulses indicative of the passage of said resonant circuit through said predetermined frequency, successively reversing the direction of tuning of said resonant circuit in response to said control pulses, and stopping said tuning variation at the maximum response point of said resonant circuit.

5. Apparatus for automatically tuning a resonant circuit to a predetermined frequency, comprising means for energizing said resonant circuit at said predetermined frequency, tuning means for varying the tuning of said circuit, reversible motor means for moving said tuning means, means responsive to passage of said tuning means through the peak resonance point of said resonant circuit for effecting reversal of said motor means, and means for stopping said tuning-means at said peak resonance point.

6. Apparatus for automatically tuning a resonant circuit to a predetermined frequency, comprising means for energizing said resonant circuit at said predetermined frequenc, reversible motor means, tuning means driven by said motor means for varying the tuning of said circuit, means responsive to passage of said tuning means through the peak resonance point of said resonant circuit for effecting reversal of said motor means, and means responsive to a predetermined number of passages through said peak resonance point for stopping said tuning means.

7. Apparatus for automatically aligning tunable circuits, comprising means for energizing the tunable circuit at a predetermined frequency, tuning means for varying the tuning of said resonant circuit, reversible motor means for driving said tuning means, means for reversing said motor means when said tuning means has passed through the peak resonance point of said re"- onant circuit, and means for stopping said tuning means at said peak resonance point.

8. Apparatus for automatically aligning tunable circuits, comprising means for energizing the tunable circuit at a predetermined frequency reversible motor means, tuning means driven by said motor means for varying the tuning of said circuit between predetermined limits on opposite sides of the point of maximum response of the tunable circuit, means for reversing said motor means when said tuning means has passed through said point of maximum response, and means responsive to a predetermined number of passages through said point of maximum response for deenergizing said motor means.

9. Apparatus for automatically aligning tunable circuits, comprising means for energizing the tunable circuit at a predetermined irequency, reversible motor means, tuning means driven said motor means for varying the tuning of said circuit between predetermined limits on opposite sides of the point of maximum response, means for deriving from said circuit a signal indicative of the passage of said tuning means through said maximum response point, and means responsive to said signal for effecting reversal of said motor means.

10. Apparatus for automatically aligning tunable circuits comprising means for energizing the tunable circuit at a predetermined frequency, reversible motor means, tuning means driven by said motor means for varying the tuning of said circuit between predetermined limits on opposite sides ci the point of maximum response, means for deriving from said circuit a signal indicative of the passage of said tuning means through said maximum response point, means responsive to said signal for effecting reversal of said motor means, and means for stopping said tuning means at said peak resonance point.

il. Apparatus for automatically aligning tunable circuits, comprising means for energizing the tunable circuit at a predetermined frequency, reversible motor means, tuning means driven by said motor means for varying the resonant frequency of said circuit, means for deriving a. signal from said circuit proportional to the instantaneous frequency thereof, means for differentiating said signal to obtain a control pulse indicative of the passage of said circuit through said predetermined frequency, means for reversing said motor means in response to said control pulse, and means for stop- 16 ping said tuning means at the maximum response point of said tunable circuit.

l2. Apparatus for automatically aligning tunable circuits, comprising means for energizing the tunable circuit at a predetermined frequency, reversible motor means, tuning means driven by said motor means for varying the resonant frequency of said circuit, means for deriving a signal from said circuit proportional 'to the instantaneous frequency thereof, means for differentiating said signal to obtain a control pulse indicative of the passage of said circuit through said predetermined frequency, means for reversing said motor means in response to said control pulse, and pulse counter means responsive to said control pulses for stopping said tuning means at the maximum response point oi said tunable circuit.

i3. Apparatus for automatically aligning tunable circuits, comprising means for energizing the tunable circuit at a predetermined frequency, reversible motor means. tuning means driven by said motor means for varying the resonant frequency of said circuit, means for deriving a signal from said circuit proportional to the instantaneous frequency thereof, means for differentiating said signal to obtain a control pulse indicative of the passage of said circuit through said predetermined frequency, means for reversing said motor mea-ns in response to said control pulse, and pulse counter means responsive to said control pulses for deenergizing said motor means after a predetermined number of reversals in the direction thereof.

14. Apparatus for automatically tuning a. resonant circuit to a predetermined frequency, comprising means for supplying oscillations at said predetermined frequency to the resonant circuit, means for varying the tuning of said resonant circuit in a predetermined direction,

means for deriving a signal from said resonant circuit proportional to the instantaneous frequency thereof, means for differentiating said signal to obtain control pulses indicative of the passage of said resonant circuit through said predetermined frequency, means for successively reversing the direction of tuning of said resonant circuit in response to said control pulses, and pulse counter means for stopping said tuning variation at the maximum response point of said resonant circuit.

15. Apparatus for automatically aligning tunable circuits, comprising means for energizing lthe tunable circuit at a predetermined frequency, reversible motor means, tuning means driven by said motor means for varying the resonant frequency of said circuit, means for deriving a signal from said circuit proportional to the instantaneous frequency thereof, means for differentiating said signal to provide a pulse of one polarity followed by a pulse of the opposite polarity, said oppositely polarized pulses occurring on opposite sides of the peak response point of said tunable circuit, means for selecting only said pulse of opposite polarity, means for increasing the slope of the leading edge of said selected pulse, and means for reversing said motor means in response to said selected pulse of increased slope.

16. Apparatus for automatically aligning tunable circuits, comprising means for energizing the tunable circuit at a predetermined frequency, reversible motor means, tuning means driven by said motor means for varying the resonant frequency of said circuit, means for deriving a signal from said circuit proportional to the instantaneous frequency thereof, means for differentiating said signal to provide a pulse of one polarity followed by a pulse of the oppon site polarity, said oppositely polarized pulses occurring on opposite sides of the peak response point of said tunable circuit, means for selecting only said pulse of opposite polarity, means for increasing the slope of the leading edge of said selected pulse, means for reversing said motor means in response to said selected pulse of increased slope, and pulse counter means responsive to said selected pulses of increased slope for de-energizing said motor means after a predetermined number of reversals in the direction thereof.

17. Apparatus for automatically tuning a resonant circuit to a predetermined frequency,

comprising means for supplying oscillations at said predetermined frequency to the resonant circuit, means for varying the tuning of said resonant circuit in a predetermined direction, means for deriving a signal from said resonant circuit proportional to the instantaneous frequency thereof, means for differentiating said signal to provide a pulse of one polarity followed by a pulse of the opposite polarity, said oppositely polarized pulses occurring on opposite sides of the peak response point of said resonant circuit, means for selecting and shaping said pulses of opposite polarity to provide steep sloped control pulses, sensing means responsive only to said control pulses for successively reversing the direction of tuning of said resonant circuit, and pulse counter means responsive to said con trol pulses for stopping said tuning variation after a predetermined number of reversals of the direction of tuning thereof.

18. The method of adjusting the tuning of a resonant circuit to a predetermined frequency which comprises the steps of, energizing said resonant circuit at said predetermined frequency, varying the tuning of said resonant circuit in a predetermined direction, de-

rlving a signal from said resonant circuit proportional to the instantaneous frequency thereof, differentiating said signal to provide a pulse cf one polarity followed by a pulse of the opposite polarity, said oppositely polarized pulses occurring on opposite sides of the peak response point of said resonant circuit, selecting only said pulse of said opposite polarity, successively reversing the direction of tuning of said resonant circuit in response to said selected pulses, and stopping said tuning variation after a predetermined number of reversals in the direction thereof.

19. The method of adjusting the tuning of a resonant circuit to a predetermined frequency which comprises the steps of, energizing said resonant circuit at said predetermined frequency, varying the tuning of said resonant circuit in a predetermined direction, deriving a signal from said resonant circuit proportional to the instantaneous frequency thereof, differentiating said signal to provide a pulse of one polarity followed by a pulse of the opposite` polarity, said oppositely polarized pulses occurring on opposite sides of the peak response point of said resonant circuit, selecting only said pulses of said opposite polarity, deriving from said selected pulses control pulses having leadw ing edges which occur just slightly after the passage of said resonant circuit through the peak response point thereof, successively reversing the direction of tuning of said resonant circuit in respon'se to said control pulses, and stopping said tuning variation after a predetermined number of reversals in the direction thereof.

KURT ENSLEIN.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 2,203,878 Rosenberg June 11, 1940 2,468,350 Sunstein Apr. 26, 1949 

